I've heard this a lot from my British relatives in Canada.
That's very interesting.
Something that happened to me recently:
We had an Away Day at work, and ended up having dinner in a tapas restaurant.
Instead of asking people what they, individually, wanted to drink, the restaurant just provided us with pitchers of Sangria, which were constantly refilled.
When someone came by with food, I asked for water, and was curtly told by the person serving that she wasn't a waitress, so she couldn't get me any.
I wasn't able to get a pitcher of water to the table until the meal was almost over. (I normally have a bottle of water in my handbag, but unfortunately, I'd neglected to refill it after taking a singing class the night before, so used up my water supply very quickly.)
In the meantime, I kept drinking Sangria to quench my thirst, which was counterproductive because the alcohol just dehydrated me more. There was lots of food, so I didn't get drunk at all, just extremely dehydrated.
(I suppose if someone couldn't drink alcohol - pregnant, on medication, alcoholic, etc., they would just have been expected to go without drinking anything?)
I caught a bad cold very soon after; I'm sure being so dehydrated that night contributed to it.
From now on, I make sure that the water bottle I carry around with me is filled to the top.